Epidemiological studies have established that hyperglycemia is responsible for the micro- and macrovascular disease that characteristically complicates human diabetes. However, the mechanism by which hyperglycemia causes vascular complications is poorly understood, in part because of the known absence of adequate animal models of diabetic complications. Indeed, no single animal model of diabetes reproduces the extensive vascular proliferative complications in the combination and intensity seen in humans. Thus, it appears that neither hyperglycemia itself nor the multiple signals activated by hyperglycemia are sufficient to induce in animals human-like vascular diabetic complications. This implies that there must be one or more genes and/or pathways necessary for the development of the diabetic vascular complications in humans that in animals differ substantially in their sensitivity to hyperglycemia and/or glycation. We have identified that the gene encoding for the complement regulatory membrane protein CD59, which inhibits formation of the membrane attack complex (MAC), is structurally different in humans and animals because hCD59 contains a glycation motif, formed by its H44 residue at approximately 5A angstroms from K41. We have shown that the K41-H44 motif makes hCD59 sensitive to inactivation by glycation, and that the H44 residue is not present in CD59 from other species. We postulate that glycation-inactivation of hCD59 due to its unique H44 residue could represent the elusive link between hyperglycemia and vascular proliferative complications of human diabetes. Consistently, high levels of glycated CD59 are found in diabetic urine, plasma and tissues; and glycated CD59 co-localizes with increased MAC deposition in kidneys, nerves and veins from diabetic subjects. Increased MAC deposition in the target tissues releases growth factors and cytokines that stimulate cell proliferation and induce synthesis of collagen type IV by glomerular mesangial cells. Increased MAC-induced mitogenic signals in diabetic tissues would act synergistically with other hyperglycemia-induced pathways causing vascular proliferative diabetic complications. In this application, we propose to use available mCd59KO and transgenic hCD59 mice to further investigate the causative role of glycation-inactivation of hCD59 in the pathogenesis of vascular proliferative complications of diabetes. We will phenotype diabetic mCd59KO, mCd59KO/hCD59WT, and mCd59KO/hCD59GIn44 variant transgenic mice for the development of human diabetic-like vascular disease, Mice will be made diabetic by injection of streptozotocin, and phenotyped by histopathology and parameters of retinal hemodynamic and renal function. We expect that in mCd59KO and in mCd59KO/hCD59WT mice, hyperglycemia will trigger a vascular proliferative response comparable to that seen in human diabetes. Instead, the hCD59GIn44 variant (resistant to glycation-inactivation) should protect mCd59KO from hyperglycemia-induced proliferative disease. We expect that these experiments will provide: 1) clear evidence for the role of glycation-inactivation of hCD59 in the pathogenesis of the proliferative vascular complications of diabetes; 2) needed animal models to study mechanism, therapy and prevention of diabetic complications; and 3) strong evidence to support future studies on complement and diabetes in humans.